Vacuum vessel



Oct. 27, 1964 c. M. ORR 3,154,138

VACUUM VESSEL Filed April 20, 1961 4 Sheets-Sheet 1 Oct. 27, 1964 c. M.ORR 3,154,138

VACUUM VESSEL Filed April 20, 1961 4 Sheets-rSheet 2 INVENTOR.

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Oct. 27, 1964 c. M. ORR 3,154,138

VACUUM VESSEL Filed April 20, 1961 4 Sheets-Sheet 3 INVENTOR.

Oct. 27, 1964 c, ORR 3,154,138

VACUUM VESSEL Filed April 20, 1961 4 Sheets-Sheet 4 INV EN TOR.

United States Patent 3,154,138 VA'CUUM VESEL Clifiord M. Orr, WesternSprings, Ill, assignor to Chicago Bridge 8: Iron Company, Chicago, Ill.,a corporation of Illinois Filed Apr. 20, 1961, Ser. No. 104,478 12Claims. (Cl. l6575) This application relates to a vacuum chamber. It isespecially concerned with an improved vacuum chamber for test systems,industrial applications, and other services wherein very low absolutepressures and a variety of temperatures can be produced.

Large size vacuum chambers capable of producing and maintainingpressures of IX torr (torrmm. Hg) or lower have a variety ofapplications. Such chambers are used in test systems, for example, forbasic research in metallurgy, chemistry, solid-state physics such aselectronic circuitry and semiconductors and others or otherinvestigatory and test programs wherein equipment and material aretested under environmental conditions simulating actual conditions whichwill be experienced during operational use of the equipment andmaterial. They also find application as vacuum furnaces, vacuum coat ingprocess vessels, freeze dryers, as well as other industrialapplications. In order to accommodate the test equipment, vessels ofthis type will have a volume of 10,000 cu. ft. or more.

In vessels of this type a pressure level consistent with the operatingrequirements must be produced. This requires the use of highly efficientvacuum pumping systems to reach the desired pressure level. Generallythe pumping systems are designed to lower the pressure so that the meanfree path of the molecules is greater than the boundaries of the chamberwhere the chambers of this invention are used in test work; this isimportant because it leaves radiation as the sole means of heattransfer.

According to this invention there is provided a low pressure chamberhaving at least one pumping manifold which functions as a common inletfor a plurality of vacuum pumps. The manifold arrangement offers greaterconductance to the molecules, by permitting radial as well as peripheralmovement of the molecules in the manifold toward the vacuum pump inlet,than individual elbow mounting of each pump and facilitates the mountingof the pumps on the test chamber. This makes it possible in manyinstances to reduce the number of pumps to produce a specified pumpingspeed.

In the drawings:

FIGURE 1 is a perspective illustration of a low pressure test facilityemploying the instant invention;

FIGURE 2 is an elevation view of an illustrative test chamber with apartial cross sectional view showing the interior of the chamber and theposition of the heat sinks;

FIGURE 3 is a plan view of the test chamber shown in FIGURE 2;

FIGURE 4 is an enlarged fragmentary view of the high conductance pumpingmanifold;

FIGURES 5 and 6 are alternative manifold systems;

FIGURE 7 is an elevation view of still another embodiment of the instantinvention; and

FIGURE 8 is a plan view of the embodiment shown in FIGURE 7.

Although the instant invention has application in a variety of services,in order to facilitate a discussion of the invention it will bespecifically described with reference to its use as a lowtemperature-low pressure test chamber.

In vacuum chambers operating at pressures of 1x l() torr the mean freepath of the molecules (the distance one molecule must travel beforestriking another) is approximately feet and only the random movements ofthe individual molecules carry them into the pumping portals. Mechanicalpumps are used for roughing and diffusion pumps or other high vacuumproducing pumps are generally used to bring the chamber to its finalpressure. The interior surfaces of such chambers are commonlyconstructed of stainless steel or other suitable metals polished tominimize outgassing in the vessel walls and to present a relativelysmooth and shiny surface to the radiant heat sink panels which in turnhave the surfaces exposed to the test article coated black. The interiorsurface of the chamber, however, is far too rough to reflect an airmolecule such that the molecules can be guided or directed in apredictable direction toward the vacuum pump inlet connections which inconventional installations consist of a plurality of ports peripherallyspaced around the chamber. Generally, the pump inlet connections arecircular openings facing the test article. An elbow from which thediffusion pump vertically depends usually contains a cold trap to reducebackstreaming of oil from the pump. The elbow mounting of a pumpcombined with a cold trap makes it necessary to provide an opening inthe chamber wall which is much larger than the entrance to the diffusionpump. In certain chambers the use of elbow mounting requires that thechamber be larger than otherwise required test space. In other chambersa staggered elbow arrangement may be required to accommodate onindividual ports all of the necessary number of vacuum pumps. Thesedisadvantages are obviated by the high conductance pump manifold systemwhich has other advantages as will be apparent from the followingdetailed description of this invention.

Referring to the drawings, in FIGURE 1 an illustrative specificembodiment of the instant invention is shown. The test chamber 10 whichfor convenience purposes is installed in a subterranean pit 11 comprisesa stiffened vertical cylinder 12 supported on tubular columns 13. Thecylinder 12 is stiffened by means of rings 12 welded to the cylinderwalls. The pit opening is enclosed by hatch covers 14 held in place atthe floor level by beams 15. The chamber It) is enclosed at the bottomby a head 16 of torispherical shape. A bottom opening 17 is provided bynozzle 18 and closure plate 19 which is removable. The chamber 13 isenlarged at the top to form a pumping manifold 20. A removable cover 21is fitted to the chamber top enclosing the top opening 22. Matingflanges 23 and 24, the former mounted on the pumping manifold 20 and thelatter comprising the peripheral edge of cover 21, are fitted withconventional double O-ring seals (not shown) or other types of sealsreusable for many closures. Cover 21 is designed to support a testplatform (not shown) suspended by the four support rods 25 and asuitable test object 26 resting on the platform in addition to theexternal pressure loading and heat sink cover. The cover is providedwith a hoisting harness 27. Suitable stiffeners 28 and 29 are used tostiffen the cover. Stiffeners 28 are radial members several of which arelifting stiffeners 28' and stiffeners 29 are annular ringsconcentrically mounted on the outer face of cover 21. A personnel accessdoor 30 is located in the cylindrical sidewall 11 near the bottom of thechamber.

The pumping system employed to effect the desired low pressurescomprises as the main pumping elements a plurality of fractionatingdiffusion pumps 35, attached to manifold 20 by nozzles 36. Suspendedwithin the ports are water-cooled traps consisting of radiation shields38 and optically dense liquid nitrogen-cooled baffles 39 to eliminatebackstreaming of the oil from the diffusion pumps into the chamber 10.Backstreaming is reduced by an optically tight liquid nitrogen trap,constructed, for example, of copper and stainless steel, mounted betweenpump 35 and chamber 10. This trap is constructed to have adequateconductance and has a central heat transfer fluid container 39surrounded by a conductively cooled drum 40, so that an oil moleculewould have to bounce off a cold surface to pass through the trap. Awater cooled radiation shield 38 is interposed between the pump and thenitrogen cooled container so that the major portion of any backstreamingoil will be condensed to a liquid and allowed to fall back into thediffusion pump. Thus the pump will not be robbed of oil, in any normaltest period, by oil held on the nitrogen trap. The water cooledradiation shield 38 also will protect the liquid nitrogen bafiie 39 fromdirect heat radiation from the diffusion pump. Automatic liquid nitrogenlevel controls are used to monitor the cold trap and keep it filled.These pumps with their traps 38 and 39 are arranged around the peripheryof the vacuum chamber and are attached to a large bell-shaped manifoldforming the top of the chamber. The bell section 20 of the chamber 10 isused as a common pumping manifold for all pumps 35. This arrangement isdesigned to optimize net speed available at the chamber and offersgreater conductance than individual elbowmounting of each pump.

Efficiency of the diffusion pumps is increased substantially by thegreater conductivity of the manifold 20 and short attachment nozzles 36compared with pumps mounted on individual elbows. Increased workingspace around the outside of the large removable cover is provided by theenlarged top head. Another feature of the large manifold is a capabilityfor the addition of a vacuum shut-off valve at each pumping port ifdesired. The enlarged manifold 20 also provides improved access to theshroud and liquid nitrogen piping inside as will hereinafter bediscussed.

The pump mounting bell is of adequate size and is designed toaccommodate additional diffusion pumps if changed conditions at a laterdate require more pumping capacity.

Backing the diffusion pumps, which are manifolded in two groups bymanifold 40, are large mechanical pumps 41 i.e., 400 c.f.m. capacitywith mechanical boosters (not shown). These pumps will be used also forroughing the chamber 10 prior to diffusion pumping and areinterconnected in such a manner that they can be used flexibly inseveral combinations to handle the gas flows at various stages of thepumping.

The internal heat transfer system or heat sink which absorbs radiantheat from objects Within the chamber employs a selected heat transferfluid and a radiant panel system. In the illustrative embodiment, a coldwall liquid cooling system is employed so that the shroud walltemperature can be very close to the normal ebullition temperature ofliquid nitrogen constantly during cold wall operations. Nitrogen orother selected cryogenic fluids, depending upon the test conditions, areused as heat transfer materials.

The cold wall system also makes provisions for heating the panels to anelevated temperature, e.g., 350- 500 F. for preconditioning bakeoutduring evacuation, in order to outgas the shroud panels and to energizethe air molecules that escape through the pump ports. If low pressuresin the 1X10 torr range are desired a complete bakeout at about 500 F.,which would include the chamber shell as well as the shroud, might benecessary. If bakeout of the chamber to this extent is performed, noadditional pumping capacity should be necessary to reach a pressure ofIX 10- torr, providing proper precautions have been taken to avoidinjury to the elastomer gaskets and to prevent opening of leaks duringbakeout.

In the shroud system shown, the shroud sections preferably aremulti-element and consist of a bottom section 56, a cylindrical lowerhalf section 51, a cylindrical upper half section 52, a conical topsection 53, and a cover section 54. Liquid feed lines 55 and vaporreturn lines 56 are connected respectively to the liquid nitrogenstorage vessel (not shown) and a vent (not shown). Flexible connectors57 are used where needed. The panel surfaces of the shroud facing thechamber walls are polished whereas the panel surfaces facing the testobjects are heat absorptive, e.g., black.

In one illustrative test chamber installation a chamber 27' in heightand having an internal diameter of 19' to provide a 15 feet diameter and20 feet high clear test area was used. To mount the diffusion pumps amanifold as illustrated in FIGURE 1 and described above having a chamber286" in diameter was used. Eight diffusion pumps in cooperation withmechanical gas ballast pumps and booster pumps were used to produce andhold a vacuum of l X lO torr.

Roughing the chamber to diffusion pump operating pressure was doneautomatically by turning on the mechanical gas ballast pumps. Thesepumps were used to evacuate the chamber to a low pressure level at whichpoint the booster pumps were turned on to augment the pumping speed. Thebooster pumps provided continuous backing to the diffusion pumpsthroughout their operatrange. Liquid nitrogen was used as the heattransfer fluid in the heat sink.

To facilitate a description of this invention the various control andinstrumentation systems and associated piping, miscellaneous accessoriessuch as heaters, Vaporizers, pumps, valves, etc., the placement of whichare obvious to those skilled in the art, are not shown. For example, inthe heat sink, controls for the preconditioning bakeout, initial coolingof the shroud with liquid nitrogen, removing liquid nitrogen from theshroud and putting it back into storage for shutting down at the end ofa test, and warming the coils if desired at time of shutdown are used.Similarly the pumping system requires suitable control andinstrumentation systems.

The subject low pressure (high vacuum) chamber provided with a highconductance pumping manifold has a variety of other uses as a vacuumfurnace, vacuum coating process vessel, freeze drying chamber, andothers. Obviously suitable accessories must be used in each instance inorder to make the chamber suitable for the selected service. Forexample, heat sources such as areing electrodes or electron beam devicesare used in vacu um furnace work; metal Vaporizers are employed invacuum coating applications, and so forth.

In fabricating the chamber of this invention, although conventionalmaterials of constructions are used, the material should be economicaland be selected to provide minimum emissivity and outgassing.Accordingly, 304 stainless steel, cupro-nickel, nickel, or coppermaterials are preferred. The heat sinks, if required for the vacuumchamber, are constructed from stainless steel, aluminum, or others.

The features of this invention are especially adaptable for relativelylarge chambers having volumes of about 1,500 to 100,000 cubic feet;however, they also find use in other size installations. The chamber canbe cylindrical as shown or can be rectangular, spherical, or othergeometrical configurations. The pumping manifold can have a crosssectional configuration similar to the test chamber or it can bedifferent. The manifold can be located at either the upper or lower endof the chamber or intermediate thereto, and one or more manifolds can beused.

The high conductance manifolds can also be used on horizontal vessels.The manifold vertically engirds the vessel and is supplied with suitableoutlets radially extending from the manifold to which the vacuum pumpsare attached. Horizontal vessels which are especially adaptable for usewith high conductance manifolds are those described in Boardman Patents2,920,784 and 2,- 672,254. The vertical vessels shown therein are alsoadaptable for use in the instant invention. In these vessels manifoldscan be installed at the intersections between the noded spheres.

As shown in FIGURE 5, the manifold 20 (in this i1- lustrative embodimentas well as in the description of the other alternative embodiments thesame numerals as previously used will be employed to identify commonelements) is positioned at an intermediate point in the wall of testchamber 10. It will be noted in this arrangement that the manifold wallsare conical surfaces as opposed to the double curvature walls shown inthe test chamber hereinbefore described. Regardless of the position ofthe manifold, it can be designed to be selfsupporting under testconditions or spaced vertical, structural support members (not shown)can be installed across the manifold opening in order to support the topof the test chamber 10 which includes a removable cover 21. In thelatter installation advantages accrue because of the elimination ofcertain stresses at the location where the supports join the shell ofthe chamber Ill. Since there is substantially no radial load at thevessel shell caused by pressure on the overhang, there is no requirementfor a heavy reinforcing ring at the shell. Only the external pressure onthe manifold is carried by the manifold. Radial forces in the manifoldmay be resisted by external reinforcing members. This is advantageous,especially for stainless steel vessels, since the shell of the manifoldcan be reinforced by more economical carbon steel members in accordancewith conventional structural design practice.

Still another embodiment of the instant invention is shown in FIGURE 6wherein the vacuum chamber 10 is a spherical vessel formed by segmentsof spheres of different radii. The bottom portion 60 is formed using oneradius of curvature, whereas the upper portion of the vessel 61, whichforms a removable top, mounted on flange 62, has a larger radius ofcurvature. In this instance, the manifold 20 takes the form of askirt-like wall encompassing the bottom section of the test chamber.Support piers 63 are peripherally spaced about the bottom wall 64- ofthe manifold 20 and vacuum pump inlet ports 65 are interspersed in thebottom Wall 64 between the support piers for mounting suitable vacuumpumps thereto. The features of this invention also are obtained by theuse of a vacuum chamber employing a high conductance manifoldarrangement shown in FIGURES 7 and 8. In this instance, the sphericalvessel which forms the vacuum chamber 10 is provided with a plurality ofhigh conductance manifolds 20 which interconnect with the interior ofthe vacuum chamber 10 by means of large circular openings 70. In thisalternative embodiment, each manifold is provided with a plurality ofvacuum pump inlets 71 to which are dependently and respectively mounteda plurality of vacuum pumps. This assembly is advantageous where it isdesirable to add special shutoff valves for the vacuum pumps. With thisarrangement, a simple closure diaphragm (not shown) mounted within theinterior of the vacuum chamber would permit the high conductancemanifolds to be isolated from the vessel interior.

The vacuum chambers are constructed to be fluid tight and leak tightpreferably having a leak no greater than about 1 1O' cc./second of airat atmospheric pressure. The number of vacuum producing pumps used suchas ion gettering or diffusion pumps will depend upon the test conditionsdesired which can be as low as l l() torr. Pressures as low as 1 10-torr can be produced with facility.

Although the subject invention has been described with reference to acomplete specific embodiment it is apparent that other variations andmodifications can be made without departing from the scope of thisinvention.

What is claimed is:

1. A large size vacuum chamber for low pressure service capable ofproducing and maintaining pressures of l 10 torr which comprises anenclosed chamber,

means for providing access to the interior of said chamber, a highconductance vacuum pumping manifold having a single inlet directlycommunicating with said chamber, said manifold having a plurality ofoutlets being free from interior obstructions to provide access betweenthe interior of said chamber and said inlet to provide means adapted tobe common to said chamber and inlet for respedti-vely connecting theretoa plurality of vacuum pumps.

2. A large size vacuum chamber for low pressure service capable ofproducing and maintaining pressures of 1 10- torr which comprises anenclosed chamber, means for providing access to the interior of saidchamber, a high conductance vacuum pumping manifold having a singleinlet directly communicating with said chamber, said manifold having aplurality of outlets adapted to be connected to vacuum pump inletslocated in the lower extremity of said manifold being free from interiorobstructions to provide access between the interior of said chamber andsaid inlets to provide a manifold common to said chamber and saidoutlets which are adapted for respectively and dependently mountingtherefrom a plurality of vacuum pumps.

3. A vessel in accordance with claim 2 in which said high conductancemanifold surrounds said chamber and opens directly thereintosubstantially continuously about its peripheral extent.

4. A vessel in accordance with claim 3 in which each of said inlets isprovided with a vacuum pump nozzle depending therefrom.

5. A large size vacuum chamber for low pressure service capable ofproducing and maintaining pressures of 1 10 torr which comprises anenclosed chamber, means for providing access to the interior of saidchamber, a high conductance vacuum pumping manifold having a singleinlet directly communicating with said chamber, said manifold having aplurality of outlets adapted to be connected to vacuum pump inlets formounting therefrom a plurality of vacuum pumps and being free frominterior obstructions to provide access between the interior of saidchamber and said inlets, said manifold being located at a terminal endof said chamber.

6. A large size vacuum chamber for low pressure service capable ofproducing and maintaining pressures of 1 10- torr which comprises anenclosed chamber, means for providing access to the interior of saidchamber, a high conductance vacuum pumping manifold having a singleinlet directly communicating with said chamber, said manifold having aplurality of outlets adapted to be connected to vacuum pump inletslocated in the lower extremity of said manifold and being free frominterior obstructions to provide access between the interior of saidchamber and said inlets to provide a common manifold for dependentlymounting therefrom a plurality of vacuum pumps, said manifold beinglocated at a terminal end of said chamber.

7. A vessel in accordance with claim 6 in which said chamber iscylindrical.

8. A large size test vessel for high vacuum testing capable of producingand maintaining pressures of 1 1O- torr which comprises a chamberdefining a test space, access means communicating with the interior ofsaid chamber, a high conductance pumping manifold opening through asingle outlet into said chamber and having disposed therein a pluralityof outlets adapted to be connected to a plurality of vacuum pump inletsto provide a common manifold for connecting a plurality of vacuum pumpstherefrom and being free from interior obstructions to provide accessbetween the interior of said chamber and said inlets, a plurality ofvacuum pumps and a heat sink located within said chamber comprising aplurality of panels having means for circulating a heat transfer fiuidtherethrough for absorbing radiant heat from objects within saidchamber.

9. A large size test vessel for high vacuum testing capable of producingand maintaining pressures of 1 10 torr which comprises a chamberdefining a test space, access means communicating with the interior ofsaid chamber, a high conductance pumping manifold opening through asingle outlet into said chamber and having disposed in the lowerextremity thereof a plurality of outlets to provide a common manifoldfor dependently mounting a plurality of vacuum pumps therefrom and beingfree from interior obstructions to provide access between the interiorof said chamber and said inlets, a plurality of vacuum pumps and a heatsink located within said chamber comprising a plurality of panels havingmeans for circulating a heat transfer fluid theretbrough for absorbingradiant heat from objects within said chamber. 7

10. A vessel in accordance with claim 9 in which said high conductancemanifold surrounds said chamber and opens directly thereintosubstantially continuously about its peripheral extent.

11. A test vessel for high vacuum testing in accordance with claim 10 inwhich said manifold is located at a terminal end of said chamber andencloses said terminal extremity.

12. A large size test vessel for high vacuum testing capable ofproducing and maintaining pressures of 1 10- torr which comprises achamber defining a test space, a high conductance pumping manifoldsurrounding said chamber and opening through a single inlet directlythereinto substantially continuously about its peripheral extent and aplurality of vacuum pump nozzles depending from said manifold and beingfree from interior obstructions to provide access between the interiorof said chamber and said inlets, said chamber being located at the upperterminal end of said test chamber enclosing said chamber end and beingprovided with access means communicating with the interior of saidchamber, a removable fluid-tight closure enclosing said access means anda heat sink located Within said chamber comprising a plurality of panelshaving means for circulating a heat transfer fluid therethrough forabsorbing radiant heat from objects Within said chamber.

References Cited in the file of this patent UNITED STATES PATENTS2,088,012 Rector July 27, 1937 2,916,536 Gruber et a1. Dec. 8, 19592,984,876 Garmy May 23, 1961

1. A LARGE SIZE VACUUM CHAMBER FOR LOW PRESSURE SERVICE CAPABLE OFPRODUCING AND MAINTAINING PRESSURES OF 1X10-4 TORR WHICH COMPRISES ANENCLOSED CHAMBER, MEANS FOR PROVIDING ACCESS TO THE INTERIOR OF SAIDCHAMBER, A HIGH CONDUCTANCE VACUUM PUMPING MANIFOLD HAVING A SINGLEINLET DIRECTLY COMMUNICATING WITH SAID CHAMBER, SAID MANIFOLD HAVING APLURALITY OF OUTLETS BEING FREE FROM INTERIOR OBSTRUCTIONS TO PROVIDEACCESS BETWEEN THE INTERIOR OF SAID CHAMBER AND SAID INLET TO PROVIDEMEANS ADAPTED TO BE COMMON TO SAID CHAMBER AND INLET FOR RESPECTIVELYCONNECTING THERETO, A PLURALITY OF VACUUM PUMPS.